To have commitments the next day, esp. in the morning, eg interviews, work, dates etc, that prevents you from doing something (usually fun and stupid) on that night.

Originated, (obviously) when having to go to bed early because school was the next day.
I'd love to get drunk and stay out all night with you guys, but it's a school night!
by ph@11u55y June 26, 2009
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An excuse to prevent from doing an immediate action or otherwise on a later date.
See, I would punch you in the face for steeling my tater tots, but you know what .... its a school night
by Larbac August 17, 2010
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(Not referring to the movie) Adult/GED Classes that are held in the evening for people who can't attend during the day due to being a parent, working or high school (if you're 18 and attending both).
People who attend to Night School (or Adult School in general) are either getting their life together by catching up on their high school credits or who immigrated to this country to be successful, learn English, and get their diploma (or GED) in order to get a good job (or head to Community College/University if they choose to) so it's the best available option if you didn't finish high school and want to get your Diploma or you can get your GED.
by Don't get me in trouble January 12, 2019
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When everybody in the group chat is sending dumb shit avoiding their responsibilities for the next day. Founded by EB, typically applies to Snapchat group chats later than 10 pm
“This some School Night Vibes right here”, Sameh says after Rajan finished talking about how he would fuck Evan, “For the boys” while procrastinating his Physics Lab
by formerjuicyback September 23, 2019
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